Replace loops with memcpy/memmove/memset in bitsetasshortlong.h

[Copilot]

Diffs

Description

Replaces element-wise loops with bulk memory operations in three bitset functions for better performance and code clarity.

Changes

• AssignLong: memmove() instead of loop (handles potential overlap)
• MakeCopyLong: memcpy() instead of loop (destination is freshly allocated)
• MakeEmptyArrayBits: memset() instead of zero-initialization loop

// Before
for (unsigned i = 0; i < len; i++)
{
    lhs[i] = rhs[i];
}

// After
memmove(lhs, rhs, len * sizeof(size_t));

All functions operate on size_t* arrays where len = BitSetTraits::GetArrSize(env). Standard library functions are available via jitpch.h.

Original prompt

File a PR against dotnet/runtime and replace plain loops in bitsetasshortlong.h with memset/memmove calls where profitable. Namely, MakeCopyLong and AssignLong

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[EgorBo]

Some visible improvements in TP, but it's possible because of the retired-instruction metric + we don't use Native PGO